Dry etching gas composition comprising sulfur-containing fluorocarbon compound and dry etching method using the same

ABSTRACT

Provided is a novel etching gas composition that comprises a sulfur-containing compound and that can selectively etch SiO 2  over low dielectric constant materials (low-k materials; SiON, SiCN, SiOCN, SiOC). 
     A dry etching gas composition comprises a saturated and cyclic sulfur-containing fluorocarbon compound that is represented by general formula (1) of C x F y S z  where x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2.

TECHNICAL FIELD

The present invention relates to a dry etching gas composition comprising a sulfur-containing fluorocarbon compound and to a dry etching method using the composition.

BACKGROUND ART

Along with the shift towards miniaturization and 3D configurations of semiconductor devices, the needs for an etching process have become increasingly demanding year after year. For this reason, the development of novel etching technology that meets such demanding needs is desired. In recent years, low dielectric constant materials, such as a carbon-containing silicon-based film represented by SiOC, have been used to reduce increasing parasitic capacitance associated with miniaturization of semiconductor devices. However, it is difficult to selectively etch, by using existing FC gases or HFC gases, a silicon oxide film or a silicon nitride film over low dielectric constant materials. In actual device fabrication, damage to a low dielectric constant film (changes in electric characteristics, such as dielectric constant, due to changes in film composition or structure caused by ion penetration or UV light generated from plasma) during dry etching poses a problem.

The present inventors have proposed that an etching gas composition containing a specific hydrofluorocarbon (1,1,4,4-tetrafluoro-1,3-butadiene) is effective as a means to resolve the above-mentioned problem (Patent Literature (PTL) 1).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2016-149451

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a novel etching gas composition that comprises a sulfur-containing compound and that can selectively etch SiO₂ over low dielectric constant materials (low-k materials; SiON, SiCN, SiOCN, SiOC).

Solution to Problem

According to the present invention the following are provided.

[1] A dry etching gas composition comprising a saturated and cyclic sulfur-containing fluorocarbon compound that is represented by general formula (1) of C_(x)F_(y)S_(z) where x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2.

[2] The dry etching gas composition according to [1], where the sulfur-containing fluorocarbon compound is 2,2,3,3,4,4,5,5-octafluorotetrahydrothiophene (C₄F₈S).

[3] The dry etching gas composition according to [1] or [2], comprising the sulfur-containing fluorocarbon compound in an amount of 1 to 100 vol %.

[4] The dry etching gas composition according to any one of [1] to [3], further comprising, in addition to the sulfur-containing fluorocarbon compound, at least one oxygen-containing compound selected from the group consisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃.

[5] The dry etching gas composition according to any one of [1] to [4], further comprising, in addition to the sulfur-containing fluorocarbon compound, at least one inert gas selected from the group consisting of N₂, He, Ar, Ne, and Xe.

[6] A dry etching method comprising plasma etching, by using the dry etching gas composition according to any of [1] to [5], a stacked structure containing at least two or more selected from the group consisting of (a1) a carbon-containing silicon-based film, (a2) a crystalline silicon film, (a3) an amorphous silicon film, (a4) a polycrystalline silicon film (polysilicon film), (a5) a silicon oxynitride film, (a6) an amorphous carbon film, (a7) a photoresist film, (a8) a silicon oxide film, and (a9) a silicon nitride film, thereby individually or simultaneously selectively etching films excluding (a6) the amorphous carbon film and (a7) the photoresist film.

[7] A dry etching method comprising plasma etching, by using the dry etching gas composition according to any of [1] to [5], a stacked structure containing at least two or more selected from the group consisting of (a1) a carbon-containing silicon-based film, (a2) a crystalline silicon film, (a3) an amorphous silicon film, (a4) a polycrystalline silicon film (polysilicon film), (a5) a silicon oxynitride film, (a6) an amorphous carbon film, (a7) a photoresist film, and (a8) a silicon oxide film, thereby selectively etching (a8) the silicon oxide film alone.

[8] The dry etching method according to [6] or [7], where etching is performed by generating a plasma of the etching gas composition according to any of [1] to [5] to form S-containing ions or active species.

[9] The dry etching method according to any of [6] to [8], where etching by the dry etching gas composition according to any of [1] to [5] is performed under plasma conditions that enable simultaneous etching of (b1) a silicon oxide film and (b2) a silicon nitride film.

Advantageous Effects of Invention

The present invention provides a novel etching gas composition that comprises a sulfur-containing compound and that can selectively etch SiO₂ over low dielectric constant materials (low-k materials; SiON, SiCN, SiOCN, SiOC).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the results of an etching test.

FIG. 2 shows the SiO₂ selectivity of an etching composition of the present invention.

FIG. 3 shows, as a bar graph, the results of the etching test relative to the etching rate of ACL.

DESCRIPTION OF EMBODIMENTS

The dry etching gas composition in the present invention encompasses a mixed gas of a saturated and cyclic sulfur-containing fluorocarbon compound that is represented by general formula (1) below or a single-component gas thereof:

C _(x) F _(y) S _(z)  General formula (1):

where x, y, and z are 2≤x≤5, y≤2x+2, and 1≤z≤2.

In view of easy handling of a dry etching gas, it is preferable to use compounds satisfying x=2 to 5, y=4 to 10, and Z=1 in general formula (1). Exemplary suitable compounds include the following.

Tetrafluorothiirane (C₂F₄S)

2,2,3,3,4,4-Hexafluorothietane (C₃F₆S)

2,2,3-Trifluoro-3-(trifluoromethyl)thiirane (C₃F₆S)

2,2,3,3,4,4,5,5-Octafluorotetrahydrothiophene (C₄F₈S)

2,3-Difluoro-2,3-bis(trifluoromethyl)thiirane (C₄F₈S)

2,2-Difluoro-3,3-bis(trifluoromethyl)thiirane (C₄F₈S)

2,2,3,3,4,4,5,5,6,6-Decafluorotetrahydro-2H-thiopyran (C₅F₁₀S)

In the dry etching gas composition in the present invention, a sulfur-containing fluorocarbon compound represented by general formula (1) having a purity of 95.0 vol % to 100.0 vol % is preferably used. A sulfur-containing fluorocarbon compound having a purity of 99 vol % or more is more preferably used, and a sulfur-containing fluorocarbon compound having a purity of 99.9 vol % or more is further preferably used. Examples of impurity components contained include N₂, O₂, CO₂, H₂O, HF, HCl, SO₂, and CH₄. Among these impurity components, H₂O, HF, HCl, SO₂, and the like are highly likely to corrode distribution channels for gases and thus preferably removed as much as possible through purification.

By using a sulfur-containing fluorocarbon compound represented by general formula (1) mixed with another fluorocarbon (FC) gas or a hydrofluorocarbon (HFC) gas, the dry etching gas composition in the present invention can further enhance the selectivity of an etching target material over materials excluding the etching target material as compared with the case without incorporating a compound represented by general formula (1). Moreover, in the case of etching a structure patterned with a material excluding the etching target material, accuracy in vertical processing is also improved.

When an etching target material is an oxygen-containing Si-based material, such as SiO₂, in a structure patterned with a material excluding the etching target material as mentioned above, it is preferable to use a compound represented by general formula (1) mixed with an etching gas, such as CF₄, CHF₃, C₂F₆, C₃F₈, C₄F₈, C₄F₆, or C₅F₈, in view of selective etching and etching with satisfactory accuracy in vertical processing. In particular, when a high selectivity is needed, it is preferable to mix with C₄F₈, C₄F₆, or C₅F₈ having a high C number.

When an etching target material is a nitrogen-containing Si-based material, such as SiN, in a structure patterned with a material excluding the etching target material, it is preferable to use, for plasma etching, a gas compound represented by general formula (1) mixed with a HFC gas, such as CHF₃, CH₂F₂, or CH₃F, in view of selective etching and etching with satisfactory accuracy in vertical processing. In particular, when a high selectivity is needed, it is also effective to use a HFC gas having a C number of 2 or more.

By adding at least one oxygen-containing compound selected from the group consisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃ to a composition containing a compound represented by general formula (1), the dry etching gas composition in the present invention can obtain the effects of suppressing excessive deposition (deposits), increasing the etching rate of an etching target, and enhancing the selectivity of the etching target over materials excluding the etching target.

In the dry etching gas composition in the present invention, at least one inert gas selected from the group consisting of N₂, He, Ar, Ne, and Xe may be added to the composition containing a compound represented by general formula (1). Among these inert gases, He, Ar, or Xe is preferably used.

Exemplary etching gases used in the method of the present invention include the following.

(a) The method can be carried out using a compound represented by general formula (1) having a purity of 90 vol % or more, and the method is preferably carried out using the compound having a purity of 99 vol % or more and is particularly preferably carried out using the compound having a purity of 99.999 vol % or more.

(b) A dry etching composition used for etching preferably contains 1 to 100 vol % of a compound represented by general formula (1).

(c) A dry etching composition used for etching preferably contains, in addition to a compound represented by general formula (1), at least one selected from the oxygen atom-containing compound group consisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃. In particular, O₂ is preferably used. The proportion of the oxygen atom-containing compound is preferably 5 to 50% and particularly preferably 10 to 35% relative to the total amount of the compound represented by general formula (1) and the oxygen atom-containing compound.

(d) A dry etching composition used for etching preferably contains, in addition to a compound represented by general formula (1) as well as in addition to or in place of the above-mentioned oxygen atom-containing compound group, at least one selected from the inert gas group consisting of rare gases and N₂. In particular, Ar is preferably used. The proportion of an inert gas contained in the etching gas composition is preferably 1 to 80 vol % and particularly preferably 50 to 75 vol %.

As a dry etching apparatus used for dry etching in the present invention, any apparatus used in the technical field concerned can be used without particular limitation. For example, an apparatus of helicon wave mode, high frequency induction mode, parallel plate configuration mode, magnetron mode, microwave mode, or the like is usable.

The dry etching method in the present invention is for vertical processing of a fine pattern wafer of a Si-based material. Accordingly, the etching apparatus needs to be an apparatus suitable for ion-assisted etching and equipped with a vacuum chamber that can reproduce low gas pressure conditions. Under low pressure conditions, particles in a plasma tend to travel in straight line and ions for irradiating a substrate reach the substrate without being blocked by other particles. Consequently, such low pressure conditions are advantageous for vertical processing since ions incident normal to the substrate increase. In the dry etching method in the present invention, the pressure inside the vacuum chamber during etching is preferably adjusted to 100 Torr to 0.1 mTorr and further preferably adjusted to 100 mTorr to 0.1 mTorr.

In the dry etching method in the present invention, a compound represented by general formula (1) is preferably introduced as a gas into a vacuum chamber of an etching apparatus. For this reason, an etching apparatus used for the dry etching method in the present invention preferably includes a mechanism for introducing the compound represented by general formula (1) as a gas and further for adjusting the amount introduced. Moreover, regarding such a mechanism, since a plurality of gas compounds including a gas compound represented by general formula (1) and other gas compounds described above, such as O₂ and Ar, are effectively used depending on the purposes in the plasma etching method in the present invention, it is preferable to include four or more mechanisms for introducing gases and for adjusting the amounts introduced.

EXAMPLES

The present working examples (etching test) used, as a plasma etching apparatus, a capacitively coupled plasma etching apparatus of parallel plate configuration from SAMCO Inc. The composition of a deposit film was determined by an SEM-EDX (scanning electron microscope/energy dispersive X-ray spectroscopy).

As a silicon oxide film (SiO_(m); m is a natural number), a SiO₂ film deposited at a thickness of 1000 nm on a silicon wafer by plasma CVD was used. As a silicon nitride film (SiN), a SiN film deposited at a thickness of 300 nm on a silicon wafer by thermal CVD was used. As an amorphous carbon film (ACL), ACL deposited at a thickness of 400 nm on a silicon wafer by plasma CVD was used. As a carbon-containing silicon film (SiOC), Black Diamond-3 (hereinafter, BD-3), which is a registered trademark from Applied Materials, Inc., deposited at a thickness of 500 nm on a silicon wafer was used. As a SiON film, SiON deposited at a thickness of 500 nm on a silicon wafer by plasma CVD was used. As a SiCN film, SiCN deposited at a thickness of 500 nm on a silicon wafer by plasma CVD was used. As a SiOCN film, SiOCN deposited at a thickness of 500 nm on a silicon wafer by plasma CVD was used.

The sample film thickness during etching was measured using an interference-mode film thickness meter. The etching conditions are shown in Table 1 below. The etching rate of a gas was calculated according to the following formula.

$\begin{matrix} {{{Etching}\mspace{14mu}{rate}\mspace{14mu}\left( {{nm}\text{/}\min} \right)} = \frac{\begin{matrix} {{{sample}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}{before}\mspace{14mu}{etching}\mspace{14mu}({nm})} -} \\ {{sample}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}{after}\mspace{14mu}{etching}\mspace{14mu}({nm})} \end{matrix}}{{etching}\mspace{14mu}{time}\mspace{14mu}({nm})}} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack \end{matrix}$

The A/B selectivity was calculated according to the following formula.

A/B selectivity=etching rate of A film (nm/min)÷etching rate of B film (nm/min)

[Etching Test]

An etching test was performed under conditions shown in Table 1 for various samples in which SiO₂, SiN, ACL, and so forth had been deposited on each silicon wafer. For etching gases, perfluorocyclobutane (1,1,2,2,3,3,4,4-octafluorocyclobutane (C₄F₈)) as a sulfur-free Comparative Example and perfluorothiacyclopentane (2,2,3,3,4,4,5,5-octafluorotetrahydrothiophene (C₄F₈S)) represented by the formula below as a sulfur-containing Example of the present invention were used.

TABLE 1 Etching Test Conditions SAMCO RIE-10NR Ar/etching gas/O₂ 50/20 (x)/**(y) [sccm] Pressure 10.0 [Pa] RF power 300 [W]

The test results are shown in FIG. 1. In FIG. 1, BD-3 represents Black Diamond 3. Ar and an etching gas were allowed to flow constantly at rates of 50 sccm and 20 sccm, respectively, while varying the rate (sccm) of oxygen (O₂). The etching of ACL started at around over 20% of the rate of oxygen relative to the total (x+y) of an etching gas (x) and oxygen (y).

In the case of the etching gas (C₄F₈S) of the Example, the etching rate of SiO₂ sharply increased with the increase in O₂ ratio to reach the maximum (approximately 80 nm/min) at the O₂ ratio of near 25%. Concerning the etching rate of SiO₂, the Comparative Example (C₄F₈) also exhibited the similar behavior. Moreover, both the etching gas (C₄F₈S) of the Example and the etching gas (C₄F₈) of the Comparative Example exhibited, although differences in etching rate values are observed, the similar behavior in which the etching rates of SiN, BD-3, SiON, SiCN, and SiOCN increase gradually with the increase in O₂ ratio and start to increase sharply at around the O₂ ratio of over 20%.

For the results in the Example and Comparative Example, the etching rate ratios of SiO₂/BD-3, SiO₂/SiON, SiO₂/SiCN, and SiO₂/SiOCN are obtained and summarized in FIG. 2. As shown in FIG. 2, the behavior in which the etching rate ratios are high at the O₂ ratio of 20% but are low at the O₂ ratio of 33% was confirmed for both the Example and the Comparative Example.

For the results in the Example and the Comparative Example, the etching rate ratios of

SiO₂/ACL, SiN/ACL, polysilicon (Poly-Si)/ACL, BD-3/ACL, SiON/ACL, SiCN/ACL, and SiOCN/ACL at the O₂ ratio of 33% are obtained and summarized in FIG. 3. FIG. 3 reveals that the etching gas of the Example exhibits, for all the materials, higher etching rate ratios relative to ACL than the etching gas of the Comparative Example.

The foregoing results revealed that remarkable differences in etching behavior exist between the Example of the present invention, in which a sulfur-containing etching gas is used, and the Comparative Example, in which a conventional sulfur-free etching gas is used. In other words, it can be concluded that the novel etching gas of the present invention has high selectivity between SiO₂ and low-k materials (SiON, SiCN, SiOCN, SiOC) similar to a conventional etching gas. Meanwhile, by adopting a novel sulfur-containing compound, the etching rate of ACL does not increase in the present invention despite the increase in O₂ ratio. Consequently, the etching selectivity between ACL and low-k materials is higher than a conventional etching gas. Moreover, by using the etching gas of the present invention in combination with a conventional etching gas, it is possible to change a difference in etching rate between ACL and low-k materials, thereby making further accurate etching possible. 

1. A dry etching gas composition comprising a saturated and cyclic sulfur-containing fluorocarbon compound that is represented by general formula (1) of C_(x)F_(y)S_(z) wherein x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2.
 2. The dry etching gas composition according to claim 1, wherein the sulfur-containing fluorocarbon compound is 2,2,3,3,4,4,5,5-octafluorotetrahydrothiophene (C₄F₈S).
 3. The dry etching gas composition according to claim 1, comprising the sulfur-containing fluorocarbon compound in an amount of 1 to 100 vol %.
 4. The dry etching gas composition according to claim 1, further comprising, in addition to the sulfur-containing fluorocarbon compound, at least one oxygen-containing compound selected from the group consisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃.
 5. The dry etching gas composition according to claim 1, further comprising, in addition to the sulfur-containing fluorocarbon compound, at least one inert gas selected from the group consisting of N₂, He, Ar, Ne, and Xe.
 6. A dry etching method comprising plasma etching, by using the dry etching gas composition according to claim 1, a stacked structure containing at least two or more selected from the group consisting of (a1) a carbon-containing silicon-based film, (a2) a crystalline silicon film, (a3) an amorphous silicon film, (a4) a polycrystalline silicon film (polysilicon film), (a5) a silicon oxynitride film, (a6) an amorphous carbon film, (a7) a photoresist film, (a8) a silicon oxide film, and (a9) a silicon nitride film, thereby individually or simultaneously selectively etching films excluding (a6) the amorphous carbon film and (a7) the photoresist film.
 7. A dry etching method comprising plasma etching, by using the dry etching gas composition according to claim 1, a stacked structure containing at least two or more selected from the group consisting of (a1) a carbon-containing silicon-based film, (a2) a crystalline silicon film, (a3) an amorphous silicon film, (a4) a polycrystalline silicon film (polysilicon film), (a5) a silicon oxynitride film, (a6) an amorphous carbon film, (a7) a photoresist film, and (a8) a silicon oxide film, thereby selectively etching (a8) the silicon oxide film alone.
 8. The dry etching method according to claim 6, wherein etching is performed by generating a plasma of the etching gas composition comprising a saturated and cyclic sulfur-containing fluorocarbon compound that is represented by general formula (1) of C_(x)F_(y)S_(z) wherein x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2 to form S-containing ions or active species.
 9. The dry etching method according claim 6, wherein etching by the dry etching gas composition comprising a saturated and cyclic sulfur-containing fluorocarbon compound that is represented by general formula (1) of C_(x)F_(y)S_(z) wherein x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2 is performed under plasma conditions that enable simultaneous etching of (b1) a silicon oxide film and (b2) a silicon nitride film. 